It is well known that patients with chronic obstructive pulmonary disease (COPD) such as emphysema, asthma, and bronchitis have limited expiratory flow and force. These patients have their airways and alveoli either partially destroyed or obstructed so that they experience great difficulty in exhaling entrapped air due to their impaired respiratory tissues. For this reason, various medical techniques or teaching methods have been developed to encourage proper expiratory maneuvers and to improve respiratory musculature. One basic technique is to instruct the patient to blow against a slight restriction or resistance. This method is commonly termed pursed lip breathing and has been found most beneficial in promoting a full long expiration of entrapped air. Various other primitive devices such as exhaling through a straw or blowing up balloons have also been used.
As the result of the limited success of the various primitive devices, a device called "blow bottles" was developed. This device consisted of two bottles locates side by side with tubings and caps attached to each bottle. One bottle was filled with water and the patient was instructed to forcibly blow into the bottle to transfer the liquid over to the second bottle. Blow bottles offered an advantage over the primitive devices in that the transfer of water acted as an incentive for exercise. However, blow bottles were often found to offer too much resistance and provided a large back pressure. Consequently, patients often became weakened, tired, and discouraged. Additionally, blow bottles were cumbersome, hard to fill and unfill, tipped easily, and were generally considered messy.
In order to avoid the problems associated with blow bottles, a device was developed which consisted of a chamber to which a length of tubing was connected. Inside the chamber was a lightweight ball. As the patient blew into the tube, the ball would rise providing an incentive. The device also had a cap with holes in it which could be used to increase expiratory effort and thus provide an increased incentive. Unfortunately, this device had several severe limitations. For example, the chamber became easily fogged due to the moisture in the exhaled air and it thus became very difficult to see the ball in the chamber. This negated the incentive provided by the rising ball. The rising ball would also frequently rise to the top of the chamber blocking off the top outtake holes and thus restricting flow through the device. In addition, the device did not give an accurate readout of expiratory flow or force being provided. It only indicated a predetermined flow even though the patient may very well have exceeded that range.
A serious shortcoming of the prior art devices discussed above was the fact that the patient's air flow rate had to increase if a corresponding increase in resistance force was desired. However, it is extremely desirable to keep the expiratory air flow rate relatively low, constant, and visibly measurable during exercise even though an increased resistance force is desired. If the flow rate is kept low, then the patient can maintain the desired long sustained exhaled breath against the fixed resistance force.
Thus, there exists in the medical field a need for a simple, inexpensive single patient use device which can measure the expiratory flow and resistance force of patients. This information can then be used to prescribe therapy such as aerosol medication more accurately. The need to provide an incentive to exercise damaged airways and expiratory musculature by the desired pursed lip type of breathing is also evident from the prior art.
In U.S. Pat. No. 4,183,361 (Russo), an inhalation exercising device is disclosed. This device includes an elongate column having a cross sectional dimension which increases in size in graduated increments through which air is drawn. An air flotation element is located within the column which rises in the column to a height corresponding to a given inhalation effort.
The use of a column having a cross sectional dimension which increases in increments has also been disclosed in the prior art in connection with flow meters. Examples of such flow meters are disclosed in U.S. Pat. No. 2,827,008 (Hodge) and U.S. Pat. No. 3,416,371 (Locke). In addition, a flow meter column having a gradually increasing cross sectional dimension is also disclosed in U.S. Pat. No. 2,099,842 (Connell).